Silt Fence & Inlet Protection in Phoenix, AZ

Silt fence and inlet protection are the sediment control measures most Phoenix construction sites lean on between grading and final stabilization. Silt fence is a trenched-in geotextile fence that slows sheet flow and lets soil settle out on the uphill side. Inlet protection keeps that soil out of catch basins and storm drains. As silt fence contractors, we install both, along with fiber rolls and perimeter controls, for builders, site contractors, pool and remodel contractors and property owners whose sites fall under a stormwater plan.

Why it matters here even with little rain

It is easy to underrate sediment control in a city that averages 7.22 inches of rain a year. The problem is how it arrives. The National Weather Service counts June 15 to September 30 as Phoenix's monsoon season, and storms in that window bring heavy localized rain and flash floods. Graded ground that has been baking for months does not soak much of that up; it sheds it, and the runoff carries fine soil straight to the curb. Winter Pacific storms add a second, gentler wet season from December through March.

When it is required

Arizona's construction general permit applies to operators of construction activity that disturbs at least an acre, and to smaller work that is one piece of a bigger planned development or sale. Construction activity there means earth disturbance such as clearing, grading, excavating and stockpiling fill. Covered sites need a stormwater pollution prevention plan that identifies pollutant sources and the control measures used, and the plan must be kept on site while work is active. If there are multiple operators, such as a developer and a contractor, each needs coverage. In Phoenix, the city's grading code notes that the NPDES/AZPDES program can add construction stormwater requirements on top of the grading permit. Our job is to put the controls where the SWPPP shows them and keep them working.

Silt fence installation done right

Most silt fence that fails was installed wrong. The fabric has to be keyed into a trench and backfilled and compacted, not just laid on the surface, or water runs under it. It goes on the contour, not straight down a slope, with ends turned uphill so flow cannot skirt around. Posts go on the downhill side. Silt fence is for sheet flow; it is not meant to sit across a concentrated channel, where a check dam or rock is the right tool. Where the ground is too hard or rocky to trench properly, we use stabilized silt fence or fiber rolls instead.

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Inlet protection

Curb inlets and area drains near a site are the last stop before the storm sewer. What we set depends on the kind of inlet and whether cars drive over it: silt fence barriers around area drains, sandbags or a gravel-filled mesh at curb openings, or filter devices under the grate. They need cleaning after storms, because a clogged filter floods the street.

Maintenance through the monsoon

Controls are only useful if they are still standing. After significant storms we check for undercutting, sagging fabric, sediment piled more than a third of the way up the fence, and knocked-over inlet devices, and we repair or replace them. Sediment that builds up behind the fence gets removed and spread on site or hauled. When the site is finally stabilized with seed, rock or landscaping, controls come out and the trench lines are smoothed.

The rainfall erosivity waiver

Arizona allows a narrow exception for some small sites. A project disturbing between one and five acres may get a waiver from the construction general permit if the rainfall erosivity factor stays below five for the whole construction period, the project is not part of a larger plan disturbing more than five acres, and it is not within a quarter mile of an impaired or outstanding state water. The factor is calculated through ADEQ's online system and the waiver has to be certified. In a dry valley, a short project scheduled outside the wet months sometimes qualifies; one running through the monsoon usually does not. Your engineer or permit preparer makes that call. If you do not have a waiver, plan on controls.

Stockpiles and entrances

Sediment does not only leave through low edges. Soil stockpiles sitting next to a curb, and the tracking that comes off tires at the site entrance, are two of the most common sources of dirt in the street after a storm. We ring stockpiles with fiber rolls or silt fence, cover the ones that will sit, and can help set up a stabilized entrance where the SWPPP shows one.

Who we work with

• Home builders and custom home contractors
• Site work and utility contractors
• Commercial general contractors
• Pool, remodel and addition contractors on tight lots
• HOAs and property managers with active projects